1. Field of the Invention
The present invention relates to a process for producing a powdery isotactic polyolefin by polymerizing a C.sub.3 or C.sub.4 olefin in the presence of a novel catalyst system. More particularly, it relates to a process for producing a powdery isotactic polyolefin such as polypropylene having reproducible high isotactic characteristic in stable with only a small amount of the catalyst system having high catalytic activity which need not to be separated after a polymerization.
2. Description of Prior Arts
Heretofore, various proposals have been found on catalysts for producing isotactic poly-.alpha.-olefin having high stereospecific characteristic and catalysts comprising a solid titanium halide and an organoaluminum compound such as dialkylaluminum halide have been well-known.
Thus, isotactic polymers having high isotactic characteristic can be obtained by using such known catalysts however, such catalysts have not enough high catalytic activity and a step for separating a catalyst residue remained in the resulting polymer is required. In order to overcome the problem, various methods have been proposed to improve remarkably a polymer productivity per a transition metal and a solid catalytic component by depositing a transition metal compound on a carrier and to eliminate substantially a step of separating the catalyst residue.
As the conventional methods, methods of using catalysts comprising a solid catalytic component supporting a titanium compound on a magnesium halide, a trialkylaluminum and an electron donor have been disclosed in Japanese Unexamined Patent Publication Nos. 16986/1973, 16987/1973 and 16988/1973.
In accordance with the conventional methods, a catalyst activity per 1 g atom of Ti is higher than that of the catalysts comprising titanium trichloride and dialkylaluminum halide, however, a crystallinity of the resulting polymer is not so high which is not satisfactory in practical operation from the view points of economical and quality aspects.
Various proposals have been also proposed on the preparations of the solid catalytic components.
For example, in accordance with the process of Japanese Unexamined Patent Publication No. 126590/1975, it has been proposed that an anhydrous magnesium halide and an organic acid ester are mixed and pulverized for 72 hours and the pulverized mixture was treated with a titanium halide, or that an anhydrous magnesium halide and a complex of an organic acid ester are mixed and pulverized for 100 hours.
It requires a long time for preparing the solid catalytic component whereby it has not been satisfactory as a preparation of a solid catalytic component in a practical operation.
In accordance with the process of Japanese Unexamined Patent Publication No. 28189/1976, an anhydrous magnesium halide is treated with a compound having active hydrogen such as ethanol and then, treated with an organic acid ester and an organometal compound and then, reacting with a titanium halide.
According to studies by the inventors, when an anhydrous magnesium halide is contacted with ethanol etc., the reaction product is remarkably swollen to form viscous slurry whereby it is not easily treated and it is difficult to maintain a uniform reaction under stirring.
Accordingly, when the solid catalytic component obtained by the proposed method is used for a polymerization of an olefin, the resulting polymer contained large amounts of coarse particles and fine particles and a size distribution is broad.
In accordance with the proposed methods, various disadvantages such as a long time is required for preparing the solid catalytic component and a complicated reaction step is required. In the preparation of the solid catalytic component by using an inorganic compound such as magnesium halide, as a carrier, a reproducibility is low and it is difficult to obtain the solid catalytic component having an uniform quality.
The inventors have considered that these disadvantages of the conventional methods are mainly caused by the preparation of the solid catalytic component, and have studied on preparations of novel solid catalytic components and have found novel solid catalytic components for producing plymers having high isotactic characteristic. Moreover, the inventors have found that a polymerization can be carried out in stable and high reproducibility to obtain high ratio of an isotactic polymer in a high catalyst activity by using a catalyst system comprising the solid catalytic component, an organoaluminum compound and an organic acid ester at suitable molar ratio of the organoaluminum compound to Ti component in the solid catalytic component and suitable molar ratio of a total of organic acid ester remained in the solid catalytic component and the added organic acid ester to the organoaluminum compound.